In this type of hot dip galvanizing line, generally, a strip (a steel plate being plated) continuously subjected to pretreatments including annealing and held at high temperature is passed between sink rolls in a molten metal coating pot and is conveyed upward. During the upward conveyance, a deposit mass (thickness of coated molten metal, or film thickness) is controlled. The strip is then cooled to normal temperature according to a predetermined cooling pattern.
While the strip is being conveyed upward, excess molten zinc adhering to the surface of the strip is wiped by gas blown from a pair of wiping nozzles (gas wiping apparatuses) situated above the molten metal coating pot in such a manner as to face each other, for example, thus controlling the deposit mass to a desired amount <see Patent Literature 1>.
For example, as shown in FIGS. 11, 12A, and 12B, a conventional gas wiping apparatus is designed so that gas supplied from the inside of a nozzle header 100 through a gas supply channel 101 to a wiping nozzle 102 is evenly blown out from a nozzle slit 105 defined between facing surfaces of upper and lower lips 103 and 104 of the wiping nozzle 102 in a width direction of a not-shown strip.
[Citation List]
[Patent Literature 1]
Japanese Patent Application Publication No. Hei 6-330275
[Patent Literature 2]
Japanese Patent No. 4020217
[Patent Literature 3]
Japanese Patent No. 3533775
[Patent Literature 4]
Japanese Patent Application Publication No. 2006-274381